Anger and (possible?) Depression

(first of all let me tell you that my English is not perfect, so sorry for any misuse of a word)
A big chunk of text follows, so if you are not interested in spending some time on this thread, please don't waste your time, it's just personal issues I would like help about.

It's been at least a year and a couple of months now I have been struggling with some problems. Because of them, I have been feeling a lot of sadness, anger and rejection. I will list a background story for these problems.

1) 1st Issue - University Colleagues
Two years ago, in 2015, I started studying at the University. I made some friends, we started hanging out. At the second day, I met another colleague who became immediately my girlfriend, up until now. After about two months I stopped going to the University, I was going about 1 day per week. Despite that I still continued talking to the friends I made and went out some times, but not a lot. They helped me with the lectures' notes and I always offered them help with homework. I was always polite and trying to be friendly ( not that I didn't want to ). It was about February 2016 that they started drifting away from me. I continued being myself though as nothing happened, I was cheerful and friendly, as my friends from back home describe me. After another 1-2 months someone from the group said they had issues with me. When I asked him what was wrong he didn't want to discuss it, I also asked 2 others, same as the first one. I then asked the last one who never seemed to have an issue with me and just told me that the first thing was just that I didn't go to lectures that often and the other thing was that when we discussed on where we want to go out for the night, I often didn't agree on the first suggestion that was made. - In my opinion, for the second reason, that is a logical thing to do, if you would prefer to go out somewhere else, you politely suggest another place. If the rest of the group didn't agree on my suggestion, I would of course follow the first suggestion, which I did. - After that, we didn't talk at all. At lectures, they didn't give me much attention when I was at the group. They were kind of aggressive towards me. In other words, they showed me they didn't like me. The second academic year came, I tried to approach them again but they stood their ground. I tried asking them to go out but they rejected me. I tried asking them again what happened but they said that they didn't want to talk about it AGAIN, though almost all of them never discussed it with me.. The whole academic year went by with me being only with my girlfriend, with them avoiding me and me trying to figure out what happened. Where I was wrong. I honestly wanted to find out what happened and apologize, try to correct things. The thought that somebody didn't like me and for a reason I didn't acknowledge was killing me inside. Up until today I see "nightmares" of them avoiding me. The feeling of rejection is awful.. The worst is that I have to see them everyday for at least 3 years now, until I finish my studies.

2) 2nd Issue - My girlfriend
She is my first relationship and I am her first one as well. For the first month we had a lot of problems, she was being very jealous and was overreacting. All my friends were telling me to dump her ( is this the word? I mean to not be with her anymore), but I was patient and I said that all relationships have problems and we will solve them and build a better relationship overtime. Which happened at a certain degree. We continued having some minor and some big problems overtime, but I think at a point it's normal for relationships. I love her and I believe she loves me. But there were sometimes that she showed me the opposite, that she doesn't care about me as much as she says. I will mention only 3 occasions, one of which has the most importance, although there have been many minor occasions.
i) March, 2017, already 1 year and a half in the relationship and my girlfriend forgot my birthday. I had to tell her on our way to University so that when someone wished me happy birthday she wouldn't go "ohh it's your birthday today" and create an awkward situation. She told me sorry at that time and at that night she came home with a cake to say sorry. My point of view: I would never forget her birthday, in fact, I plan what special present to give her and show her my love. I wrote a poem for her on a wooden board, I planned a trip for her.. I don't understand how you forget the birthday of someone you love and who you are everyday with.
ii) There have been times that I told her there were some issues troubling me and sometimes ,for a reason or another, maybe we were angry at each other due to an argument, she didn't care to ask me what those issues were. Not even when we made up. I always had to ask her how it is possible not to care to ask about the issues of your partner.
iii) The most important. A year ago, I got hospitalized because I was very sick. My girlfriend, as well as my 2 best friends who study at the town I study, came to see me in the afternoon. When the night came, my girlfriend told me she had to go home to sleep so she could go to the University the next morning and asked me if that was okay by me.. Of course I would tell her to stay with me. I don't want her to do something because she is told to but because she cares and wants to do it. So she left and went home. This was troubling me because if it was her in my position, I wouldn't leave the hospital at all. I would stay there all night in case she needed something and I wouldn't even think of going to the University.

These are my two major "issues", that I believe cause me the most anger and internal sadness. I don't show my sadness to others, not even my best friends. They do know the existence of these problems but they don't know 100% how I feel. Also, about the anger, I often get angry at my girlfriend, letting my anger out. I don't hit her or something, but I steel feel bad for sometimes yelling at her and I tell her sorry for that. But I would prefer I would even do that.

Thank you for reading, any advice would be appreciated!

I get the impression that "being liked" is very important for you, but I wonder if maybe you're trying too hard to be liked. If your friends don't like you, and if they've treated you unfairly, then why still try to please them? Do you want to be friends with people who would treat you badly? Move on and find other friends, and accept that not everyone is going to like you. As long as you're happy with who you are, and you know you've tried your best to be a good person, then it's their loss.

Personally, I don't see forgetting a birthday as a big thing, and I think you may be overreacting, but that's just my opinion. If you mentioned to your girlfriend that you have some issues, why are you waiting for her to ask what they are? Why not just tell her? This implies that perhaps you're trying to make her "prove" that she loves you?

It's difficult to tell without knowing you personally, but I get the impression that maybe you're trying to get other people (including your friends and girlfriend) to make you feel like you matter in the world... In other words, you are looking for reassurance that you're a decent person, but you're trying too hard which might be causing them to behave the way they do. By constantly seeking approval and love, you might end up pushing people away. When we experience fragile self-esteem, we often end up "testing" the people close to us, and trying to get them to prove that we're worth something, that they care about us, etc. Unfortunately, while it is common for people to do this, it never really works. I may be completely wrong, and maybe this isn't the case. But if it is, then I would honestly recommend seeking professional counselling in person to figure out why your self-esteem is fragile, and looking at ways to fix that.